Journal of Cancer Research and Therapeutics Medknow Publications on behalf of the Association of Radiation Oncologists of India (AROI) ISSN: 0973-1482 EISSN: 1998-4138 Vol. 5, Num. 4, 2009, pp. 263-266

Journal of Cancer Research and Therapeutics, Vol. 5, No. 4, October-December, 2009, pp. 263-266

Original Article

Survey of patient dosimetry for head and neck cancer patients undergoing external radiotherapy treatment: A study from northeastern hospitals of India

Sharma ArunkumarB, Singh TomchaTh, Singh KhelendraN, Gartia RK

Department of Radiotherapy, RIMS, Imphal

Correspondence Address:Department of Radiotherapy, Regional Institute of Medical Sciences, Imphal - 795 004, Manipur
arunsb2000@yahoo.co.uk

Code Number: cr09063

PMID: 20160359

DOI: 10.4103/0973-1482.59903

Abstract

Keywords: Dosimetry, iodized salt, thermoluminescence/optically stimulated luminescence dosimeter

Introduction

The induction of malignant neoplasm by irradiation is so uncommon that it seldom plays any role in therapeutic decision making. However, there is always a chance of second cancer occurring after radiotherapy for a variety of cancers among long-term survivors. It is also reported that about 0.65% of patients who received radiotherapy entries were readmitted on an average after 16.4 ± 6.6 years due to a newly developed cancer. ^[1] Theoretically, the risk of these potential hazards (i.e., mutagenesis and carcinogenesis) is dose dependent. ^[2],[3],[4] The importance of dosimetry of patients during radiotherapy is now well known and well documented. ^{[1],[5],[6],[7],[8]} Therefore, dosimetry in radiotherapy planning is aimed to deliver a sufficient high dose at the tumor site avoiding unnecessary irradiation in as much as possible to the healthy tissue and organs that surround the tumor. The northeastern region (NER) of India is the remotest part of the country where few radiotherapy centers are working with ⁶⁰ Co teletherapy as the main treatment source of external radiation. Cancer of the head and neck region is relatively quite high in this region (NER) of the country. Moreover, there is lack of sufficient data about the dose distribution over different organs/parts of the body during the radiotherapy procedure in head and neck cancer patients. The present study, in the context of the NER to determine the dose distribution over various parts of the body during radiotherapy ( ⁶⁰ Co teletherapy) at three different hospitals, has therefore been performed for this particular type of cancer. Reference doses can be determined by common dosimetry methods and thermoluminescence (TL) as well as optically stimulated luminescence (OSL) dosimeters are two of them. The work carried out at the Luminescence Dating Laboratory, Manipur University, has shown that commercial Indian salts, like Taja and Shudh brands, are good materials for TL dosimetry ^[9],[10] and OSL dosimeter. ^[11],[12] With the help of such iodized salt-based dosimeters, the dose distribution over different important anatomical points, namely, forehead, thyroid, arm, gonad, etc. has been evaluated.

Materials and Methods

Head and neck cancer

There are about seven radiotherapy (RT) centers in operation in the NER and a few more are coming up. Head and neck cancer is the most common type and among the cases, pharynx, larynx, and tongue are observed frequently occupying top positions. Three centers were identified for the study (referred to as A, B, and C) and 35 patients (12 patients from A, 10 from B, and 13 from C) were selected for the evaluation of dose over various parts of the body when treated from external sources ( ⁶⁰ Co). Cases of cancer of nasopharynx were 11 in number, larynx 9, tongue 9, pyriform sinus 3, oropharynx 2, and mouth 1.

TL/OSL dosimeter

A common Indian iodized salt (Shudh brand-manufactured by Nirma Limited, Ahmedabad, India) was used as the dosimeter. It was crushed to fine powder and pressed as pellets of 40 ± 4 mg by applying pressure of 1 ton for 1 min (diameter is 8 mm and thickness ~ 1 mm). All the pellets were given thermal treatment at 500°C for 30 min. These pellets were further encapsulated with air- and light-tight materials (such as small, black plastic bag). The reliability of the pellet in terms of its reproducibility as well as reusability has already been discussed. ^[9] The integrated TL responses of pellets within ±5% for two test doses (2 and 4 Gy) of g-irradiation ( ⁶⁰ Co) were selected. These were further exposed to 2 Gy and correction factors for each pellet were obtained. Two sets of pellets were then exposed to a dose ranging between 0.5 Gy and 12 Gy. A calibration curve of TL output versus dose (Gy) was then generated from the exposure obtained from RT center A [Figure - 1]. A similar curve for OSL output versus dose was also obtained from RT center B [Figure - 2].

TL/OSL measurement

TL and OSL measurements were carried out on the Riso TL/OSL (model TL/OSL-DA-15) reader that can accommodate as many as 48 samples mounted on the turntable. All the TL measurements were recorded in the flowing N ₂ atmosphere with a uniform heating rate of 5°C/s. OSL measurements were recorded at room temperature (~20°C) for 40 s using blue LED light (470 nm). The power of the blue LED used is 45 mw. The photomultiplier tube used is EMI 9635 in the operating voltage of 950 volts with optical filter Schott UG-11 in conjunction with Schott BG-39 for filtering out the unwanted radiation. The combination allows transmission in the wavelength range 300-400 nm, a suitable filtration for the present dosimeters.

The time gap between the g-irradiated pellets and TL/OSL measurement was 10-14 days. During this time interval, fading is negligible (< 1%). ^[13] A second readout was performed to record the background radiation which includes the back body radiation.

Riso TL/OSL reader is a commercial system used globally for dating and dosimetry. ^[14]

Results

The dose reconstruction of 35 radiotherapy (teletherapy) patients treated at the head and neck region was performed at some selected anatomical points as shown in [Figure - 3]. The average percentage of the absorbed dose that was obtained on a particular day from fractionated radiotherapy is shown in [Table - 1]. However, the doses to the reference points for the whole treatment procedure may be obtained by multiplying the fractionated dose on a particular day and the number of fractions for that particular treatment procedure.

Discussion

It is observed that the percentage of deviation of the measured entrance dose as compared with the calculated value (using the Plato sunrise treatment planning system) goes as much as 7.4% while that of the exit dose goes further down to 14% for the RT center C whereas RT centers A and B were 5.6% and 6.5% at the entrance and 9.6% and 12.1% at the exit respectively. Similar findings were reported by Julian et al.^[7] as 6% on the beam entry and 11% on the beam exit for the head and neck cancer cases. Standard statistical tests ^[15],[16] (test of equality of variances and means) were performed for the deviations of the entrance dose obtained from the TL dosimetry at the three centers for checking any significance differences of the outcomes. The finding is placed in [Table - 2]. Variances of deviations of the entrance dose of A, B, and C centers are insignificant at the 5% level of probability. It means that this variation (i.e., response of reproducibility of pellets) may be observed at any center. Analysis of means inferring the inter dose comparison shows that they are also insignificant at the 5% level of probability indicating comparable dosimetry among the three centers. Similar results are also observed for the data of the exit dose obtained from TL dosimetry at the three centers.

The average percentage of the absorbed dose [Table - 1] at the forehead is maximum for the treatment of the pharynx (~2.1 ± 0.5%), tongue/mouth (~2.1 ± 0.3%), and then larynx (~1.3 ± 0.5%). An absorbed dose of ~1.0 ± 0.1% at the forehead was reported by Miah et al.^[5] for the treatment of larynx using the telecobalt source which is in well agreement with our finding. Chest gets maximum value for the treatment of the larynx (~2.7 ± 0.8%) than the rest of the treatments (~1.7 ± 0.3%). The likely reason for a higher scatter reading in the chest may be that we have more advanced head and neck cancers and we more often treat up to the lower neck as low down as the intraclavicular line. The other reference points get close values for different cases of head and neck treatment as abdomen 1.0 ± 0.3%, gonad 0.8 ± 0.2%, arm 0.9 ± 0.3%, and leg 0.4 ± 0.1%. So, one may expect about 2% of the delivered dose at forehead and in the chest region, about 1% at the gonad, abdomen, and arm and about 0.5% at leg from the treatment of head and neck cancer cases using external radiotherapy (Co-60).

A common dose range given to head and neck cases is observed as 60-70 Sv. During the treatment procedure, the modification of treatment protocol is also practiced depending on the response of the therapy. Histograms of doses at reference points evaluated from direct as well as scatter radiation for a total cumulative dose of 65 Sv at the target from three RT centers are placed in [Figure - 4]. None of the patients, other than the target, received on an average of 2 Sv of dose from stray radiation. The forehead and chest (i.e., near target) received the maximum dose (1-2 Sv) whereas for the rest of the reference points, it was observed to be less than 1 Sv. Thus, for head and neck cancer treatment studied at these three RT centers, an average dose of 1.17 ± 0.39 Sv at forehead, 1.24 ± 0.39 Sv at chest, 0.65 ± 0.20 Sv at abdomen, 0.52 ± 0.13 Sv at gonad, 0.59 ± 0.20 Sv at arm, and 0.26 ± 0.07 Sv at leg areas for a cumulative dose of 65 Sv at the target may be expected. The average height and weight of patients under consideration were 150 ± 8 cm and 48 ± 7 kg respectively.

Conclusions

This survey of patient dosimetry for head and neck cancer cases from the NER radiotherapy centers of India may be summarized as follows:

Maximum dose received from stray radiation, i.e., other than the target is about 1.5 Sv at forehead/chest (i.e., near the target), and remaining other reference points received below 1 Sv of dose during the entire treatment procedure.

Interdose comparison of the three hospitals is insignificant at 5% level of probability to accept that dosimetry among them is not significantly different at that level of probability.

The average dose reconstruction profiles of the three centers are in good agreement indicating the confidence in the measurement.

Acknowledgments

The authors wish to thank DST, Seismology Division, for supporting the Luminescence Dating Laboratory, Manipur University, whose facility has been used for the work. Thanks are also due to medical physicists working in the northeastern region, namely, Mr. Devan Singh and Mr. K. Pao for their kind cooperation and Dr. S. N. Singh of Luminescence Dating Laboratory, Manipur University, for technical help.

References

1.	Wolfgang D, Thomas H. Cancer induction by radiotherapy: dose dependence and spatial relationship to irradiated volume. J Radiol Prot 2002;22:A117-21.  Back to cited text no. 1
2.	Little MP, Muirhead CR, Boice Jr JD, Kleinerman RA. Using multistage models to describe radiation-induced leukaemia. J Radiol Prot 1995;15:315-34.   Back to cited text no. 2
3.	Albrecht MK. Radiation risk-historical perspective and current issues. J Radiol Prot 2002;22:A1-10.  Back to cited text no. 3
4.	Little MP, Vathaire F de, Charles MW, Hawkins MM, Myirhead CR. Variations with time and age in the relative risks of solid cancer incidence after radiation exposure. J Radiol Prot 1997;17:159-77.  Back to cited text no. 4
5.	Miah FK, Ahmed MF, Begum Z, Alam B, Chowdhury Q. Dose distribution over different parts of cancer patients during radiotherapy treatment in Bangladesh. Rad Prot Dosim 1998;77:199-203.  Back to cited text no. 5
6.	Ahmed MF, Begum Z, Miah FK, Chowdhury Q. Dose distribution over different organs of some retinoblastoma cancer patients undergoing radiotherapy. J Med Phys 1999;24:190-4.  Back to cited text no. 6
7.	Julian M, Grazyna K, Jerzy K, Aleksander G. An Analysis of effectiveness and accuracy of ionization, semiconductor and thermoluminescent detectors used in total body irradiation. Jour Med Phys 1996;21:10-3.  Back to cited text no. 7
8.	Petoussi N, Zankl M, Williams G, Veit R, Drexler G. GSF -Reports 5/87. 1987.  Back to cited text no. 8
9.	Gartia RK, Arunkumar SB, Ranita U. Thermoluminescence response of some common brands of iodised salt. Indian J Eng Mat Sci 2004;11:137-42.  Back to cited text no. 9
10.	Arunkumar SB, Basanta ST, Gartia RK. Critical evaluation of goodness of fit of Computerised Glow Curve Deconvolution. Indian J Pure Appl Phys 2004;42:492-7.  Back to cited text no. 10
11.	Nabadwip SS, Arunkumar SB, Gartia RK. Iodised salt (NaCl:I): A candidate for OSL dosimetry. Proceedings of NSLA-2003. NPL, New Delhi, India: February 12-14. 2003. p. 368-71.  Back to cited text no. 11
12.	Arunkumar SB, Gartia RK, Khelendra SN. OSL dosimetry over different parts during RT treatment: The case study of RIMS hospital, Proceedings of NCLA-2006. Amravati, Maharastra, India: February 7-9. 2006. p. 158-60.  Back to cited text no. 12
13.	Arunkumar SB, Gartia RK, Nabadwip SS. Fading correction of NaCl(I) TLD. Int J Modern Phy B 2006;20:1077-86.  Back to cited text no. 13
14.	Botter-Jensen L. Luminescence techniques: instrumentation and methods. Radiat Meas 1997;27:749-68.  Back to cited text no. 14
15.	Kenett RS, Zacks S. Modern Industrial Statistics. Duxbury Press. An International Thomson Publishing Company; 1998.  Back to cited text no. 15
16.	Weisstein EW. CRC concise Encyclopedia of Mathematics. CRC Press LLC; 1999.  Back to cited text no. 16

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